1. Field of the Invention
The present invention relates to integrated circuits, and more specifically to a method and apparatus for adjusting the strength of output buffers.
2. Related Art
Output buffers are often used in integrated circuits to drive external device/load (e.g., another integrated circuit) based on data received from another source. In general, output buffers need to drive external loads with sufficient strength (e.g., the amount of current) to ensure that the data is accurately transferred to the external devices within a pre-specified time duration.
The desired strength of output buffers depends on several factors. Some of such factors include manufacturing process, supply voltage, temperature, speed and external load. Some of the relevant factors may change while an integrated circuit is in use/operation, thereby further changing the load (desired strength) and/or the strength of the output buffer.
Output buffers are often designed with a high strength corresponding to a worst case scenario, for example, weak/slow manufacturing process, maximum ambient temperature, maximum load, and maximum speed of operation. As a result, such an output buffer can drive the external load for any combination of the factors.
One problem often encountered with such output buffers designed for worst case is an undesirable amount of switching noise. Switching noise generally refers to undesirable noise generated due to the transition of the signal at the output node of an output buffer. In addition, a buffer designed for worst case may switch faster than required, which may cause more switching noise.
Such a switching noise is often propagated to other components/parts of an integrated circuit through a common substrate. Switching noise is generally undesirable at least in that undesirable interference may be presented to signals in the surrounding components. At least due to such a reason(s), it may be desirable to adjust the strength of an output buffer.